Image forming apparatus

Abstract

A heater has a main heater block arranged in a reference area corresponding to a sheet having a reference size and a sub-heater block arranged in an outer-side area. An outer-side sheet sensor detects the sheet at a location within the outer-side area between a transfer device and a fixing device. The control device, depending on target size information representing a size of a target sheet, controls a power supply state between a first power supply state and a second power supply state. The control device, in a case in which the target size information represents a size exceeding the reference size, and depending on whether or not the outer-side sheet sensor detects the target sheet, further controls a conveying interval between the target sheet and a next sheet following the target sheet to one of a first interval and a second interval longer than the first interval.

The invention claimed is: 
     
         1 . An image forming apparatus, comprising:
 a sheet conveying device configured to be able to sequentially convey a plurality of sheets;   a transfer device configured to transfer a toner image onto each of the plurality of sheets being conveyed;   a fixing device including a heater configured to heat the toner image on each of the plurality of sheets sequentially conveyed from the transfer device, and a pressure portion configured to press each of the plurality of sheets toward the heater;   a sheet detection portion arranged on an upstream side of the fixing device in a sheet conveying direction, and configured to detect each of the plurality of sheets being conveyed;   a control device configured to control power supply to the heater and the sheet conveying device;   a main temperature sensor;   a sub-temperature sensor;   a first thermal protector; and   a second thermal protector, wherein   the heater includes a main heater block arranged in a reference area corresponding to a sheet having a reference size in a main direction crossing the sheet conveying direction, and a sub-heater block arranged in an outer-side area adjacent to the reference area in the main direction and corresponding to a sheet having a size larger than the reference size;   the outer-side area includes a first outer-side area and a second outer-side area adjacent to both sides of the reference area;   the sub-heater block includes a first sub-heater block arranged in the first outer-side area and a second sub-heater block arranged in the second outer-side area;   the main temperature sensor detects a temperature of the main heater block;   the sub-temperature sensor detects a temperature of the first sub-heater block;   the first thermal protector is arranged at the main heater block and is configured to electrically cut off a power supply line to the main heater block when the temperature of the main heater block exceeds an allowable temperature;   the second thermal protector is arranged at the second sub-heater block and is configured to electrically cut off a power supply line to the sub-heater block when a temperature of the second sub-heater block exceeds an allowable temperature;   the second thermal protector is arranged at a line-symmetrical position with respect to a position of the sub-temperature sensor with respect to a center line passing through a center of the reference area in the main direction and along the sheet conveying direction;   the sheet detection portion includes an outer-side sheet sensor configured to detect the sheet at a position within the outer-side area in the main direction between the transfer device and the fixing device;   the control device acquires target size information representing a size of a target sheet reaching the fixing device;   the control device, depending on whether the target size information represents a size within the reference size or a size exceeding the reference size, further controls a power supply state of supplying power to the heater so as to be one of a first power supply state in which power is supplied only to the main heater block, and a second power supply state in which power is supplied to the main heater block and the sub-heater block;   the control device, in a case in which the target size information represents a size exceeding the reference size, and depending on whether or not the outer-side sheet sensor detects the target sheet, further sets a conveying interval between the target sheet and a next sheet following the target sheet to one of a first interval and a second interval longer than the first interval; and   the control device stops power supply to one or both of the main heater block and the sub-heater block when a detected temperature of one or both of the main temperature sensor and the sub-temperature sensor exceeds a preset upper limit temperature.   
     
     
         2 . The image forming apparatus according to  claim 1 ,
 wherein   the control device controls a power supply amount supplied to the main heater block and the sub-heater block by feedback control of the temperature detected by the main temperature sensor.   
     
     
         3 . The image forming apparatus according to  claim 1 ,
 wherein
 the control device controls a power supply amount supplied to the main heater block by feedback control of the temperature detected by the main temperature sensor, and controls a power supply amount supplied to the sub-heater block by feedback control of the temperature detected by the sub-temperature sensor.